Thin-walled pipes, as they are used, for example, in exhaust, air conditioning and ventilation technology, are increasingly provided with profiled sheet metal flanges, which are drawn together with the above-mentioned clamping rings and are connected to each other in this way.
In general, a screw having a correspondingly long screw length or a lever lock is sufficient to close this clamping ring quickly and easily. This type of connection saves considerable assembly time compared to the time that is required for connecting flanges made of flat or angle steel, which must be connected to each other with a plurality of individual screws.
The terminal flanges can be profiled sheet metal flanges that are placed onto the ends of the pipes or are integrally formed thereon. Clamping rings suited for connecting these flanges have different cross-section profiles, depending on the type of seal. The most widely used clamping rings have V-shaped cross-sectional profiles. U-shaped cross-sectional profiles or other shapes are found less frequently.
The simplest form of an integrally formed flange is the stay flange. To produce these flanges, the pipe end is folded outward at a suitable angle or crimped by means of rolling tools. To connect such flanges configured as stay flanges, a simple clamping ring configured as a clamping ring for spiral-seam tubes.
While this type of connection is inexpensive, it is neither air-tight nor stable.
To produce air-tight and more stable connections, clamping rings having a V-shaped or U-shaped cross-section are better suited, into which a sealing tape to produce the air tightness can be inserted.
The sealing tape can also be inserted between the surfaces of the terminal pipe flanges facing each other.
Clamping rings of this type are also in principle suited for connecting flanges having circular cross-sections, which are typically crimped at the ends of the pipes.
If higher tightness and stability are required, conical pipe flanges are better suited, which are connected to each other by placing on clamping rings having a V-shaped cross-section. These pipe flanges can also either be placed on or integrally formed. With this type of connection, the sealing effect is achieved by inserting sealing tape either in the apex region or between the flange surfaces facing each other.
These conical flange connections have therefore proven very useful in practice because during assembly the pipe ends are not only pulled axially toward each other, but are also radially oriented by means of the flange ring. This dual function is met best if the exterior surfaces of the pipe flanges and accordingly the interior surfaces of the clamping rings have an inclination of approximately 60° in relation to the pipe wall.
Despite the advantages described above, however, also this type of connection is still associated with considerable deficiencies, namely:                a) When drawing the clamping ring together, considerable frictional resistance must be overcome. The reason for this is that the conical exterior pipe flange surfaces and the corresponding interior clamping ring surfaces rest against each other across large surfaces on the entire circumference, resulting in considerable friction because the surfaces are generally galvanized, which is to say rough. Once the clamping ring is closed enough that the above-mentioned surfaces have a force-fit contact, the tensile force of the only clamping force is no longer sufficient to completely draw the clamping ring together across the entire circumference. Rather, the tension force develops exclusively in the region of the clamping lock, because it is not forwarded into the more remote region of the surfaces due to the high friction. As a result, the clamping ring and consequently the pipe flange are deformed unevenly.        As a result of the uneven tension force distribution, the seal glued into the apex of the clamping ring having a V-shaped cross-section is compressed with varying pressure levels, leading to a worse sealing effect.        Attempts are made during assembly to achieve an improved, meaning more symmetrical, distribution of the tension force by lightly tapping on the outer circumference of the clamping ring with a rubber mallet. Apart from the fact that this procedure delays the assembly, this measure does not offer sufficient guarantee for even tension force distribution as well as even sealing.        b) A further disadvantage is that also at the face flange surfaces the above-mentioned frictional resistance occurs, particularly if a friction-increasing seal is glued onto one of these flange surfaces. Once the clamping ring is being closed, the flanges are drawn axially toward each other by means of their beveled flanges. The seal between the flange surfaces is compressed before the radially centering effect occurs in the region of the apex of the clamping ring with the V-shaped cross-section. The consequence is that the pipe axes and therefore the pipe walls are not aligned, but rather offset from each other. Even with further tightening of the clamping ring they cannot be aligned any more because this is prevented by the friction of the flange surfaces and/or of the seal.        As a result, a step forms on the inside of the pipe when the connection is closed, the step interfering with the air flow and leading to deposits in this region, making subsequent cleaning more difficult.        The same problem occurs even in flange connections in which a foamed rubber seal is glued into the apex of the clamping ring, because the pressure of the comparatively soft seal is not sufficient to align the pipe axes against the friction of the flange surfaces.        c) A further problem for clamping rings having V-shaped cross-sections is that the alignment of the pipe flanges to be connected to each other, namely the transverse displacement of the two pipe flanges in the radial direction up to the V-apex of the clamping ring of the seal glued in this region, entirely depends on when the faces of the flanges come in contact. Even minor form errors of these flanges, which are relatively frequent with such sheet metal profiles, mean that the penetration depths of the two pipe flanges no longer agree, resulting in the axial shifting effect explained in        b). In order to take these circumstances into account, which is to say to compensate for the deviations, a high, soft and flexible seal must be used, which is glued into the V-apex of the clamping ring. For this application, foam seals are suited. While these seals provide a sufficient sealing effect for common mean air pressures found in ventilation technology, they are completely unsuited for extremely high pressures or even for water-tight and oil-tight seals.        